Method and system for fuel vapor control

ABSTRACT

A method and system for fuel vapor control in a hybrid vehicle (HEV). The HEV fuel vapor recovery system includes a fuel tank isolation valve, which is normally closed to isolate storage of refueling from storage of diurnal vapors. The method for fuel vapor control includes selectively actuating the fuel tank isolation valve during interrelated routines for refueling, fuel vapor purging, and emission system leak detection diagnostics to improve regulation of pressure and vacuum the HEV fuel vapor recovery system.

FIELD

The present application relates to fuel vapor purging in a hybridvehicle.

BACKGROUND AND SUMMARY

Hybrid vehicles, such as plug-in hybrid vehicles, may have two modes ofoperation: an engine-off mode and an engine-on mode. While in theengine-off mode, power to operate the vehicle may be supplied by storedelectrical energy. While in the engine-on mode, the vehicle may operateusing engine power. By switching between electrical and engine powersources, engine operation times may be reduced, thereby reducing overallcarbon emissions from the vehicle. However, shorter engine operationtimes may lead to insufficient purging of fuel vapors from the vehicle'semission control system. Additionally, refueling and emission controlsystem leak detection operations that are dependent on pressures andvacuums generated during engine operation may also be affected by theshorter engine operation times in hybrid vehicles.

Various strategies have been developed to address fuel vapor control andmanagement in hybrid vehicle systems. Example approaches includeseparating storage of refueling vapors from storage of diurnal vapors byadding a fuel tank isolation valve (FTIV) between a fuel tank and a fuelvapor retaining canister, and allowing refueling vapor purging to thecanister during refueling events, and engine-on purging methods. Theseparation of diurnal and refueling vapors allows a pressure to begenerated in the fuel tank, while application of alternative vacuumsources allows a vacuum to be generated in the canister.

One example approach for fuel vapor management is shown by Suzuki et al.in U.S. Pat. No. 7,032,580 B2. Therein, a control system determines ifthe fuel tank pressure is above a predetermined value while a purgingfrom the carbon canister to the engine intake is occurring. If the fueltank pressure is greater than the predetermined value, a pressurecontrol valve between the fuel tank and the carbon canister is opened topermit purging of fuel vapors from the fuel tank. Opening of an exhaustgas recirculation valve is adjusted based on the opening of the pressurecontrol valve to decrease an amount of fuel injected to the engine andsuppress fluctuation of the air-fuel ratio. The pressure control valveis closed after a duration, based on pressure in the fuel tank and thepurge flow rate, has elapsed.

However, the inventors herein have recognized potential issues with thisapproach. As one example, under conditions where the average fuel tankpressure is very high, such as in hybrid vehicle fuel systems, thepressure valve may open more frequently, or for longer durations,leading to more frequent engine air-fuel ratio fluctuations. Forexample, if the fuel tank is normally sealed from the canister, theambient temperature is high, and the hybrid vehicle has been operated inthe engine-off mode for a long duration, the fuel tank pressure may besignificantly higher than that of the carbon canister. As a result,controlled release of fuel vapors from the fuel tank, to dissipate thefuel tank pressure, while the canister purge valve is open may bedifficult to achieve, and flooding of the engine with excessive vaporsmay occur. Such flooding may lead to engine stumbles and stalls, anddegrade engine performance.

The above issue may be at least partly addressed by a method that allowsfor coordination of purging fuel vapors from the fuel tank with purgingof fuel vapors from the canister, by regulating opening of a FTIV, tomaintain a canister pressure and a fuel tank pressure, without floodingthe engine. In one embodiment, the method includes, operating a fuelvapor recovery system coupled to an engine intake, the fuel vaporrecovery system including a fuel tank coupled to a canister through afirst valve, the canister coupled to the engine intake through a secondvalve, the canister further coupled to a vacuum accumulator. The methodmay comprise, during a purging condition, purging a first amount of fuelvapors from the canister to the engine intake; and after purging thefirst amount, purging a second amount of fuel vapors from the fuel tankto the canister, the second amount adjusted based on the first amount.

In one example, a fuel vapor recovery system for a hybrid vehicle maycomprise a fuel tank coupled to a canister via a fuel tank isolationvalve (FTIV). The canister may be coupled to the engine intake via acanister purge valve (CPV). The canister may be further coupled to avacuum accumulator via a vacuum accumulator valve (VAV). As such, theFTIV may be maintained closed during vehicle operation and may beselectively opened during refueling and diurnal purging conditions. Bymaintaining the FTIV closed, the fuel vapor circuit may be divided intoa canister side and a fuel tank side. Refueling vapors may be retainedin the canister on the canister side of the circuit while diurnal vaporsmay be retained in the fuel tank on the fuel tank side of the circuit.

A first pressure sensor may be coupled to the fuel tank to estimate apressure of the fuel tank side of the circuit, while a second pressuresensor may be coupled to the carbon canister to estimate a pressure ofthe canister side of the circuit. Based on input from various sensors,such as the pressure sensors, and further based on vehicle operatingconditions, a controller may adjust various actuators, such as the CPV,the FTIV, and a canister vent valve (CVV), to enable fuel tankrefueling, purging of stored fuel vapors, and leak detection in the fuelvapor recovery system.

In one example, the controller may determine purging conditions are metwhen the canister pressure is above a first predetermined thresholdwhile the vehicle is operated in an engine-on mode. The controller maythen open the CPV to purge refueling vapors stored in the carboncanister to the engine intake. Once the carbon canister pressure hasfallen below the first threshold, the CPV may be closed and thecontroller may determine if a fuel tank pressure is above a secondpredetermined threshold. The controller may accordingly open the FTIV topurge diurnal vapors stored in the fuel tank to the carbon canister. Theduration of opening of the FTIV may be determined as a function of thecanister pressure, so that the controller may close the FTIV as thepressure of the canister approaches the first threshold.

In such an approach, operation of the FTIV may be tightly regulatedduring purging to maintain a pressure in the carbon canister that isbelow the first threshold for purging and prevent flooding of the engineduring a purging operation. Additionally, regulated bleeding of fuelvapors from the fuel tank may partially curb the high pressurefluctuations experienced in the fuel tank. Further, the present approachmay allow fuel tank and canister pressures to equilibrate faster. Assuch, fuel tank refueling may be unsafe when fuel tank pressures arehigh. Thus, by equilibrating fuel tank and canister pressures faster,purging may be better coordinated with refueling operations, forexample, by reducing a delay time between receiving a refueling requestevent and opening of a fuel tank door, after fuel tank pressuredissipation, to receive fuel.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic depiction of a hybrid vehicle.

FIG. 2 shows an example embodiment of the fuel system and fuel vaporrecovery system of FIG. 1.

FIG. 3 shows a high level flow chart for operating the fuel vaporrecovery system of FIG. 2.

FIG. 4 shows a high level flow chart for operating the fuel vaporrecovery system during a refueling event.

FIG. 5 shows a high level flow chart for operating the fuel vaporrecovery system during a purging event.

FIGS. 6-8 show high level flow charts for performing leak detectionoperations on the fuel vapor recovery system of FIG. 2.

FIGS. 9-11 show maps depicting example fuel tank and/or canisterpressures which may occur during leak detection operations.

FIG. 12 shows a map depicting example changes in fuel tank temperaturewhich may occur during leak detection operations.

DETAILED DESCRIPTION

The following description relates to a fuel vapor recovery system for ahybrid vehicle, such as the vehicle system of FIG. 1, and a method ofmonitoring flow of fuel vapors and/or air though the fuel vapor recoverysystem. As shown in FIG. 2, the fuel vapor recovery system may include afuel tank isolated from a canister by a fuel tank isolation valve(FTIV), the canister further coupled to an engine intake by a canisterpurge valve (CPV). In this way, refueling vapors may be stored in thecanister while diurnal vapors are retained in the fuel tank, dividingthe fuel vapor circuit into a canister side and a fuel tank side. Avacuum accumulator may be included in the fuel vapor recovery system toprovide a vacuum source to the canister. The vacuum accumulator may beconfigured to generate and store vacuum during engine-on conditions andengine-off conditions, such as from the engine and/or from a brakebooster pump. A controller may receive signals from various sensorsincluding pressure, temperature, fuel level, and refueling door positionsensors, and accordingly regulate actuators, including various valves ofthe fuel vapor recovery system, by performing various routines duringvehicle operation, such as refueling, fuel vapor purging, and leakdetection, as shown in FIGS. 3-8. Example changes in system pressuresand temperatures, as detected by various sensors in the fuel vaporrecovery system, are depicted in the maps of FIGS. 9-12. By applyinginter-related strategies, engine-on and engine-off vehicle operations,refueling, fuel vapor purging, and leak detection operations may bebetter coordinated, thereby improving fuel vapor management in hybridvehicles.

Referring to FIG. 1, the figure schematically depicts a vehicle with ahybrid propulsion system 10. Hybrid propulsion system 10 includes aninternal combustion engine 20 coupled to transmission 16. Transmission16 may be a manual transmission, automatic transmission, or combinationsthereof. Further, various additional components may be included, such asa torque converter, and/or other gears such as a final drive unit, etc.Transmission 16 is shown coupled to drive wheel 14, which may contact aroad surface.

In this example embodiment, the hybrid propulsion system also includesan energy conversion device 18, which may include a motor, a generator,among others and combinations thereof. The energy conversion device 18is further shown coupled to an energy storage device 22, which mayinclude a battery, a capacitor, a flywheel, a pressure vessel, etc. Theenergy conversion device may be operated to absorb energy from vehiclemotion and/or the engine and convert the absorbed energy to an energyform suitable for storage by the energy storage device (in other words,provide a generator operation). The energy conversion device may also beoperated to supply an output (power, work, torque, speed, etc.) to thedrive wheel 14 and/or engine 20 (in other words, provide a motoroperation). It should be appreciated that the energy conversion devicemay, in some embodiments, include a motor, a generator, or both a motorand generator, among various other components used for providing theappropriate conversion of energy between the energy storage device andthe vehicle drive wheels and/or engine.

The depicted connections between engine 20, energy conversion device 18,transmission 16, and drive wheel 14 may indicate transmission ofmechanical energy from one component to another, whereas the connectionsbetween the energy conversion device 18 and the energy storage device 22may indicate transmission of a variety of energy forms such aselectrical, mechanical, etc. For example, torque may be transmitted fromengine 20 to drive the vehicle drive wheel 14 via transmission 16. Asdescribed above energy storage device 22 may be configured to operate ina generator mode and/or a motor mode. In a generator mode, system 10 mayabsorb some or all of the output from engine 20 and/or transmission 16,which may reduce the amount of drive output delivered to the drive wheel14, or the amount of braking torque from brake system 30, which includesbrake booster 34 and brake booster pump 32, to the drive wheel 14. Suchoperations may be employed, for example, to achieve efficiency gainsthrough regenerative braking, increased engine efficiency, etc. Further,the output received by the energy conversion device may be used tocharge energy storage device 22. Alternatively, energy storage device 22may receive electrical charge from an external energy source 24, such asa plug-in to a main electrical supply. In motor mode, the energyconversion device may supply mechanical output to engine 20 and/ortransmission 16, for example by using electrical energy stored in anelectric battery.

Hybrid propulsion embodiments may include full hybrid systems, in whichthe vehicle can run on just the engine, just the energy conversiondevice (e.g. motor), or a combination of both. Assist or mild hybridconfigurations may also be employed, in which the engine is the primarytorque source, with the hybrid propulsion system acting to selectivelydeliver added torque, for example during tip-in or other conditions.Further still, starter/generator and/or smart alternator systems mayalso be used.

From the above, it should be understood that the exemplary hybridpropulsion system is capable of various modes of operation. For example,in a first mode, engine 20 is turned on and acts as the torque sourcepowering drive wheel 14. In this case, the vehicle is operated in an“engine-on” mode and fuel is supplied to engine 20 from fuel system 100(depicted in further detail in FIG. 2). Fuel system 100 includes a fuelvapor recovery system 110 to store fuel vapors and reduce emissions fromthe hybrid vehicle propulsion system 10.

In another mode, the propulsion system may operate using energyconversion device 18 (e.g., an electric motor) as the torque sourcepropelling the vehicle. This “engine-off” mode of operation may beemployed during braking, low speeds, while stopped at traffic lights,etc. In still another mode, which may be referred to as an “assist”mode, an alternate torque source may supplement and act in cooperationwith the torque provided by engine 20. As indicated above, energyconversion device 18 may also operate in a generator mode, in whichtorque is absorbed from engine 20 and/or transmission 16. Furthermore,energy conversion device 18 may act to augment or absorb torque duringtransitions of engine 20 between different combustion modes (e.g.,during transitions between a spark ignition mode and a compressionignition mode).

The various components described above with reference to FIG. 1 may becontrolled by a vehicle control system 40, which includes a controller12 with computer readable instructions for carrying out routines andsubroutines for regulating vehicle systems, a plurality of sensors 42,and a plurality of actuators 44. Select examples of the plurality ofsensors 42 and the plurality of actuators 44 are described in furtherdetail below, in the description of fuel system 100.

FIG. 2 shows an example embodiment 200 of the fuel system 100 and fuelvapor recovery system 110 of FIG. 1. Engine 20, coupled to a fuel system100, may include a plurality of cylinders (not shown). Engine 20 mayreceive intake air through intake manifold 60 which may lead to anexhaust passage (not shown) that routes exhaust gas to the atmosphere(as indicated by arrows). It will be appreciated that the engine intakeand exhaust manifolds may be additionally coupled to an emission controldevice and/or a boosting device.

Fuel system 100 may include a fuel tank 120 coupled to a fuel pumpsystem for pressurizing fuel delivered to the injectors of engine 20(not shown). It will be appreciated that fuel system 100 may be areturn-less fuel system, a return fuel system, or various other types offuel system. Vapors generated in fuel system 100 may be routed to a fuelvapor recovery system 110 via a first conduit, vapor line 112, beforebeing purged to intake manifold 60 via a second conduit, purge line 118.

The fuel tank 120 may hold a plurality of fuel blends, including fuelwith a range of alcohol concentrations, such as various gasoline-ethanolblends, including E10, E85, gasoline, etc., and combinations thereof. Asdepicted in FIG. 2, fuel tank 120 includes a fuel level sensor 122 whichmay comprise a float connected to a variable resistor. Alternatively,other types of fuel level sensors may be used. Fuel level sensor 122sends fuel level input signals to controller 12.

Fuel tank 120 also includes a refueling line 116, which is a passagewaybetween the refueling door 126, which includes a refueling valve (notshown) on the outer body of the vehicle and the fuel tank, wherein fuelmay be pumped into the vehicle from an external source during arefueling event. Refueling door sensor 114 coupled to refueling door 126may be a position sensor and send input signals of a refueling door openor closed state to controller 12. Refueling line 116 and vapor line 112may each be coupled to an opening in fuel tank 120; therein fuel tank120 has at least two openings.

As noted above, vapor line 112 is coupled to the fuel tank for routingof fuel vapors to a fuel vapor canister 130 of the fuel vapor recoverysystem 110. It will be appreciated that fuel vapor recovery system 110may include one or more fuel vapor retaining devices, such as one ormore of a fuel vapor canister 130. Canister 130 may be filled with anadsorbent capable of binding large quantities of vaporized hydrocarbons(HCs). In one example, the adsorbent used is activated charcoal.

Canister 130 may receive fuel vapors from fuel tank 120 through vaporline 112, as vapor line 112 is connected at an opposing end to anopening in canister 130. Canister 130 includes two additional openings,wherein a vent 136 and a purge line 118 are coupled, such that canister130 has three openings. While the depicted example shows a singlecanister, it will be appreciated that in alternate embodiments, aplurality of such canisters may be connected together.

Opening of vapor line 112 is regulated by a fuel tank isolation valve(FTIV) 124. In an alternate embodiment FTIV 124 may be mounted directlyto fuel tank 120 at the attachment point of vapor line 112. As such,during vehicle operation, FTIV 124 may be maintained in a closed state,such that refueling vapors may be stored in the canister on the canisterside of the fuel vapor circuit and diurnal vapors may be retained in thefuel tank on the fuel tank side of the fuel vapor circuit. FTIV 124 maybe operated on by controller 12 in response to a refueling request or anindication of purging conditions. In these instances, FTIV 124 may beopened to allow diurnal vapors to enter the canister and relievepressure in the fuel tank. Additionally, FTIV 124 may be operated oncontroller 12 to perform specific steps of leak detection, such asapplying a pressure (positive pressure or vacuum) from fuel tank 120 tocanister 130 during a first leak detection condition, or applying avacuum from canister 130 to fuel tank 120 during a second leak detectioncondition (described in further detail in FIGS. 6-8). In one example,FTIV 124 may be a solenoid valve and operation of FTIV 124 may beregulated by the controller by adjusting a duty cycle of the dedicatedsolenoid (not shown).

A first fuel tank pressure sensor, such as a fuel tank pressuretransducer (FTPT) 128, may be coupled to fuel tank 120 to provide anestimate of a fuel tank pressure. For example, FTPT 128 may be includedin the top portion of fuel tank 120. In an alternate embodiment, FTPT128 may be coupled to vapor line 112 on the fuel tank side of the fuelvapor circuit. Additionally, fuel tank 120 may include a temperaturesensor 140 to provide an estimate of a fuel tank temperature.Temperature sensor 140 may be coupled to FTPT 128, as depicted in FIG.2. In an alternate embodiment, temperature sensor 140 may be coupled tothe fuel tank in a distinct location from FTPT 128. Each of pressure(P_(FT)) and temperature (T_(FT)) signals from FTPT 128 and temperaturesensor 140, respectively, are received by controller 12.

Fuel vapor recovery system 110 may communicate with the atmospherethrough vent 136, extending from canister 130. Canister vent valve (CVV)132 may be located along vent 136, coupled between canister 130 and theatmosphere, and may adjust flow of air and vapors between fuel vaporrecovery system 110 and the atmosphere. Operation of the CVV 132 may beregulated by a canister vent solenoid (not shown). Based on whether thefuel vapor recovery system is to be sealed or not sealed from theatmosphere, the CVV may be closed or opened. Specifically, controller 12may energize the canister vent solenoid to close CVV 132 and seal thesystem from the atmosphere, such as during leak detection conditions.

In contrast, when the canister vent solenoid is at rest, the CVV 132 maybe opened and the system may be open to the atmosphere, such as duringpurging conditions. Further still, controller 12 may be configured toadjust the duty cycle of the canister vent solenoid to thereby adjustthe pressure at which CVV 132 is relieved. In one example, during arefueling vapor storing operation (for example, during a fuel tankrefilling and/or while the engine is not running), the canister ventsolenoid may be de-energized and the CVV may be opened so that air,stripped of fuel vapor after having passed through the canister, can bepushed out to the atmosphere. In another example, during a purgingoperation (for example, during a canister regeneration and while theengine is running), the canister vent solenoid may be de-energized andthe CVV may be opened to allow a flow of fresh air to strip the storedvapors of the activated charcoal. Additionally, controller 12 maycommand CVV 132 to be intermittently closed, by adjusting operation ofthe canister vent solenoid, to diagnose reverse flow through the fuelvapor recovery system. In yet another example, during leak detection,the canister vent solenoid may be energized to close CVV 132, while CPV134 and FTIV 124 are also closed, such that the canister side of fuelvapor recovery circuit is isolated. In this way, by commanding the CVVto be closed, the controller may seal the fuel vapor recovery systemfrom the atmosphere.

Fuel vapors released from canister 130, for example during a purgingoperation, may be directed into intake manifold 60 via purge line 118.The flow of vapors along purge line 118 may be regulated by canisterpurge valve (CPV) 134, coupled between the fuel vapor canister and theengine intake. In one example, CPV 134 may be a ball check valve,although alternative check valves may also be used. The quantity andrate of vapors released by the CPV may be determined by the duty cycleof an associated solenoid (not shown). As such, the duty cycle of thecanister purge valve solenoid may be determined by the vehicle'spowertrain control module (PCM), such as controller 12, responsive toengine operating conditions, including, for example, an air-fuel ratio.By commanding the canister purge valve to be closed, the controller mayseal the fuel vapor recovery system from the engine intake.

An optional canister check valve 136 may also be included in purge line118 to prevent intake manifold pressure from flowing gases in theopposite direction of the purge flow. As such, the check valve may benecessary if the canister purge valve control is not accurately timed orthe canister purge valve itself can be forced open by a high intakemanifold pressure (such as, during boosted conditions). An estimate ofthe manifold absolute pressure (MAP) may be obtained from a MAP sensor(not shown) coupled to engine intake manifold 60, and communicated withcontroller 12. As such, check valve 136 may only permit theunidirectional flow of air from canister 130 to intake manifold 60. Inthe event of high pressure air entering the purge line from intakemanifold 60, canister check valve 136 may close, thereby preventing thepressure in canister 130 from exceeding design limits. While thedepicted example shows the canister check valve positioned between thecanister purge valve and the intake manifold, in alternate embodiments,the check valve may be positioned before the purge valve. A secondcanister pressure sensor, such as canister pressure transducer (CPT)138, may be included in purge line 118, coupled between canister 130 andCPV 134 to provide an estimate of a canister pressure. In alternateembodiments the CPT may be coupled to the vent between the canister andthe CVV, or may be coupled to the vapor line between the canister andthe fuel tank on the canister side of the fuel vapor circuit. Signalsindicating canister pressure (Pc) are received by controller 12.

Fuel vapor recovery system 110 also includes vacuum accumulator 202coupled to fuel vapor canister 130. In one example, vacuum accumulator202 may be coupled through vacuum line 208 to purge line 118, betweencanister 130 and the CPV 134. In other example embodiments, the vacuumline may be coupled to the vapor line between the canister and the FTIV.Application of vacuum from the vacuum accumulator to the canisterthrough vacuum line 208 is regulated by opening or closing vacuumaccumulator valve (VAV) 204, as commanded by controller 12. VAV 204 maybe selectively opened by controller 12 during emission leak detectionoperations, such as when insufficient engine-off natural vacuum isavailable, to provide additional vacuum for leak detection. For example,VAV 204 may be selectively opened during a secondary leak detectionsubroutine implemented under a condition wherein the absolute pressureof the fuel tank is less than a threshold, as further elaborated in FIG.9.

In one embodiment, vacuum accumulator 202 may be coupled to intakemanifold 60 through conduit 206, and may accumulate vacuum when thehybrid vehicle is operated in the engine-on mode. That is, theaccumulator may store an amount of engine vacuum for later use.Additionally, or optionally, a venturi 302 may be coupled to vacuumaccumulator 202 by venturi vacuum line 304. The venturi may be mountedat various locations on the body of the hybrid vehicle that receive airor exhaust flow during vehicle motion and operation. For example, theventuri may be mounted on the underside of the vehicle body. In anotherexample, venturi 302 may be coupled to the exhaust manifold, for examplealong the tailpipe, such that vacuum may be generated due to the flow ofexhaust through the venturi. In yet another example, as depicted,venturi 302 may be mounted in the exhaust pathway of a brake boosterpump 32 coupled to a brake booster 34 of the vehicle brake system 30.Herein, during brake application, vacuum may be generated due tooperation of the brake booster pump and flow of brake booster pumpexhaust through the venturi. In one example, by coupling the venturi tothe exhaust pathway of the brake booster pump, rather than directlycoupling the vacuum accumulator to the brake booster pump, the brakebooster pump may not be exposed to fuel vapors. In still otherembodiments, vacuum accumulator 202 may be directly coupled to brakebooster pump 32, wherein vacuum may be generated by operating the brakepump, and stored in the vacuum accumulator for use in leak detectionroutines.

Controller 12 may be configured to regulate various operations of thefuel vapor recovery system by receiving signals from sensors, such aspressure, temperature, and position sensors, and commanding onactuators, such as opening and closing of valves or the refueling door.For example, controller 12 may carry out various routines for leakdetection, refueling, and fuel vapor purging, as shown in FIGS. 4-8.Specifically, the various routines for the fuel vapor recovery systemmay be better coordinated by controller 12, for example, by performing ahigher-level vapor recovery system routine, as shown in FIG. 3, whichmay strategically implement each of the various routines depending onthe operating conditions of the vehicle, such as engine-on or engine-offoperations, and pressure and temperature inputs from sensors. Forexample, if a refueling routine is implemented, controller 12 maydisable a purging routine.

An example higher-level vapor recovery system routine 300 is depicted inFIG. 3. Herein, at 302 it may be determined whether the vehicle is on oroff, that is, whether or not the vehicle is operational. In one example,this may be detected by a key command sensor and/or motion sensor forthe vehicle (not shown). If the vehicle is not being operated, thecontroller 12 may enable a leak detection routine at 303, describedfurther in FIG. 6. Leak detection may additionally be regulated by otherfactors recorded by the controller, such as time elapsed since a lastleak detection routine occurred. In alternate embodiments, leakdetection methods may be implemented while the vehicle is on, but in anengine-off mode of operation.

If the controller receives a signal that the vehicle is on, at 304 it isdetermined if the vehicle is in an engine-on mode or an engine-off mode.If the vehicle is operating in an engine-off mode, the controller mayimplement the commands shown at 308. Specifically, the controller maymaintain a closed state for each of the FTIV and the CPV. That is,diurnal vapors may be stored in the fuel tank while refueling vapors mayare stored in the canister. Additionally, purging routines may belimited for the duration of the engine-off mode of operation. Optionallyat 310, during the engine-off mode of operation, vacuum may be stored inthe vacuum accumulator. Specifically, the controller may maintain theVAV closed while vacuum is generated at the venturi coupled to thevacuum accumulator. As previously elaborated, vacuum may be generateddue to flow of air and/or exhaust through the venturi irrespective onengine operation mode, such as due to flow of ambient air during vehiclemotion or exhaust flow from the brake booster pump.

If the vehicle is operating in an engine-on mode at 304, then at 306,the FTIV and CPV may be maintained in closed positions. At 310, thecontroller may maintains the VAV closed while accumulating vacuum due toflow of air and/or exhaust through the coupled venturi. As such, inaddition to the vacuum accumulation strategies described above, vacuummay also be generated by coupling the vacuum accumulator to the engineintake manifold.

Next, at 314, purging conditions may be confirmed. Purging conditionsmay include detection of engine-on operations, a signal from the CPTthat the canister pressure is above a predetermined threshold (such as,threshold₂ of FIG. 5), and/or a signal from the FTPT that the fuel tankpressure is above a threshold (such as, threshold₃ of FIG. 5). Ifpurging conditions are confirmed, a purging routine (further depicted inFIG. 5) may be commanded at 315. If purging conditions are not met, at318, the controller may maintain the closed positions of the FTIV andthe CPV.

At 316, independent of the vehicle operation mode, it may be determinedif a fuel tank refueling is requested by the user. If no refuelingrequest is received, the routine may end. In one example, a refuelingrequest may be determined by the controller based on user input througha button, lever, and/or voice command. In response to a refuelingrequest, a refueling routine (further depicted in FIG. 4) may beimplemented at 320. However, if the refueling request is received duringa purging operation (such as, while purging operations of step 315 arebeing performed), at 320, the purging routine may be temporarilydisabled for the duration of the refueling event, for example, bytemporarily commanding the CPV closed. With this, the routine may end.

In this way, purging and refueling operations may be better coordinatedso as to enable refueling only when fuel tank pressures are within asafe range, while staggering purging operations with refueling so as toreduce excess refueling fuel vapor flow into the engine intake.

Now turning to FIG. 4, a refueling routine 400 is shown. At 402, a userrefueling request may be confirmed by the controller. In response to therefueling request, the controller may disable engine operations at 406.At 408, purging operations may be disabled, for example, by(temporarily) maintaining the CPV in a closed position. At 410, the FTIVmay be opened and the CVV may be maintained open. Herein, by opening thevapor line between the fuel tank side and the canister side of the fuelvapor circuit, pressure in the fuel tank may be relieved. For example,if a high pressure exists in the fuel tank, air and fuel vapors may flowfrom the fuel tank through the vapor line and into the canister. Inanother example, if a vacuum exists in the fuel tank, air may flow fromthe canister through the vapor line and into the fuel tank. In bothexamples, pressures of the fuel tank and the canister may go towardequilibrium, such that the fuel tank may be safely and easily opened.

At 412, it may be determined whether the absolute value of the fuel tankpressure is below a predetermined threshold (threshold₁). If so, at 416,refueling may be enabled. If the absolute value of the fuel tankpressure is greater than threshold₁, the controller may delay opening ofthe refueling door in command 414, until the fuel tank pressure fallsbelow threshold₁. The controller may enable refueling by commanding arefueling door to open, for example, by de-energizing a solenoid in therefueling door to enable door opening. The vehicle operator may thenhave access to the refueling line and fuel may be pumped from anexternal source into the fuel tank until refueling is determined to becomplete at 418.

Because the FTIV may remain open during the refueling operation,refueling vapors may flow through the vapor line and into the carboncanister for storage. Until refueling is complete, refueling operationsmay be maintained at 420. If refueling is completed at 418, for examplebased on input from the fuel level sensor, the refueling door may beclosed at 422, for example by energizing the refueling door solenoid. Inresponse to refueling door closing, at 424, the FTIV may be closed inthereby ensuring that refueling vapors are stored in the canister sideof the fuel vapor circuit. Therein, the refueling routine may beconcluded. In this way, refueling may be enabled only when fuel tankpressures are within a safe range, and improving coordination ofrefueling with purging.

Now turning to FIG. 5, a purging routine 500 is depicted. Purgingroutine 500 may be enabled in response to purging conditions being met(at 314 of FIG. 3), such as when the vehicle is operated in an engine-onmode and a refueling event is not requested. At 502, while the vehicleis operated in the engine-on mode, it may be determined if a canisterpressure (Pc), for example as estimated by the CPT, is above apredetermined threshold for purging (threshold₂). If the canisterpressure is above the threshold, and a refueling request is received at504, then at 506, purging operations may be disabled at least for theduration of refueling, and refueling operations (FIG. 4) may be enabledat 508. Specifically, CPV may be maintained closed for the duration ofthe refueling event.

If the canister pressure is above the threshold, and no refuelingrequest is received at 504, then at 510, the controller may command theCPV to open while maintaining the FTIV closed and the CVV open. At 512,air may flow from the atmosphere into the canister through the vent anda first amount of refueling vapors stored in the canister may be purgedto the engine intake manifold. Thus, during the purging of the firstamount of fuel vapors from the canister to the intake, no fuel vaporsmay be purged from the fuel tank to the canister. The first amount ofpurging may include an amount of fuel vapors (e.g., fuel mass), aduration of purging, and a rate of purging. As such, the CPV may bemaintained open until the canister pressure, for example as estimated bythe CPT, falls below a threshold (threshold₂), at 514, at which time theCPV may be closed at 516.

At 518, purging conditions of the fuel tank may be determined, forexample, based on a fuel tank pressure (such as estimated by the FTPT)being above a threshold for purging (threshold₃). If the fuel tankpressure is below threshold₃, the fuel tank may not require purging andtherefore the FTIV may be maintained in a closed position at 520 and thepurging routine may end. If the fuel tank pressure is above threshold₃,the controller may command the FTIV to open at 522, and at 524 may bleeddiurnal vapors, such as a second amount of fuel vapors, from the fueltank through the vapor line into the canister. The second amount ofpurging may include an amount of fuel vapors (e.g., fuel mass), aduration of purging, and a rate of purging. The second amount may bebased on the first amount purged from the canister. For example, as anamount and duration of purging of the first amount of fuel vapors fromthe canister increases, the second amount purged from the fuel tank maybe increased. During the bleeding of diurnal vapors from the fuel tank,the canister pressure may be monitored and the FTIV may remain open (at528) at least until the canister pressure reaches a threshold. At 526,it may be confirmed that the canister pressure is above a lowerthreshold but below an upper threshold (threshold₄). If the canisterpressure is greater than or equal to threshold₄, the controller maycommand the FTIV to close at 530 and the purging routine may becompleted.

In one example, the threshold pressure for purging the fuel tank may bebased on the threshold pressure for purging the canister. For example,threshold₄ may be determined as a function of threshold₂ and may be lessthan threshold₂ to ensure that a first amount of fuel vapors, purgedfrom the canister to the engine, is greater than a second amount of fuelvapors, bled from the fuel tank to the canister. This method ofoperation may curb pressure fluctuations in the fuel tank by relievingsome pressure during purging operations, while limiting the amount andrate of fuel vapor flow to the engine intake manifold. Additionally,this method may change the pressure vs. temperature curve of the fueltank during cool downs due to removal of fuel mass, affecting subsequentleak detection subroutines (described below) and diurnal vaporgeneration.

In this way, by limiting the amount and rate of fuel vapors that flow tothe engine during purging, engine flooding may be prevented andvariability in vehicle operation experienced by the vehicle operator maybe reduced. In alternate embodiments, both fuel tank pressure andcanister pressures may be monitored throughout the purging routine.Additionally, the FTIV may be opened concurrently with the CPV. In stillother embodiments, the same threshold may be used for commanding bothfuel tank purging and canister purging.

In one example, the vehicle may be a hybrid vehicle with an engine thatis selectively operated in response to a battery state of charge. Thus,in one example, the vehicle may be operated with the engine-on, forexample, due to the state of charge of the vehicle battery being below athreshold. During vehicle motion, a venturi coupled to the underside ofthe vehicle body may be configured to generate vacuum due to the flow ofair there-through. The generated vacuum may be stored in a vacuumaccumulator coupled to the venturi. Similarly, during vehicle operation,vacuum may be generated and stored in the venturi during brakeapplication. For example, the venturi may be coupled to the outlet of abrake booster pump such that exhaust flow the brake booster pump may beflown through the venturi and advantageously used to generate a vacuum.The stored vacuum may be used at a later time, for example, during leakdetection operations.

During the vehicle operation, a controller may keep the FTIV closed andthe CPV closed to retain refueling fuel vapors in the canister anddiurnal fuel vapors in the fuel tank. When purging conditions are met,for example, when a canister pressure exceeds a threshold due to storageof fuel vapors therein, the controller may open the CPV while keepingthe FTIV closed, to thereby purge an amount of fuel vapors to the engineintake. After purging fuel vapors from the canister, that is, when thecanister pressure has dropped below a threshold, the controller may thenproceed to purge fuel vapors from the fuel tank to the canister and/orengine intake. In one example, the controller may determine whether topurge the diurnal fuel vapors from the fuel tank to the canister and/theintake based on engine operating conditions, and/or a fuel tankpressure. For example, when the fuel tank pressure at the time ofpurging is above a threshold, the controller may determine that a largeramount of fuel vapors are to be purged from the fuel tank, and mayaccordingly open the FTIV while keeping the CPV open to thereby purgefuel vapors to the canister and further on to the engine intake. Inanother example, when the fuel tank pressure at the time of purging isbelow the threshold, the controller may determine that a smaller amountof fuel vapors are to be purged from the fuel tank, and may accordinglyopen the FTIV while closing the CPV to thereby purge fuel vapors to thecanister and not to the engine intake. Once purging operations arecompleted, the controller may re-seal the fuel tank and canister byclosing the FTIV and CPV to resume storing fuel vapors in the canisterand retaining diurnal vapors in the fuel tank. In this way, purging offuel vapors from the canister and the fuel tank may be coordinated.

In another example, during vehicle operation (that is, during anengine-on or engine-off mode), a refueling request may be received, suchas due to a fuel level in the fuel tank falling below a threshold. Assuch, if the refueling request is received during a purging operation,the purging may be delayed for at least the duration of the refueling,to advantageously coordinate refueling operations with purgingoperations. To enable refueling, the engine controller may first turnthe engine off, if it was previously turned on. A refueling door may beopened to enable a fuel pump nozzle to be inserted to receive fuel inthe fuel tank. However, before opening a refueling valve coupled to thedoor, to ensure operator safety during refueling, the controller mayverify that the fuel tank pressure is below a threshold. If the fueltank pressure is above the threshold, the controller may open the FTIVto release the retained diurnals into the canister and delay opening ofthe fuel valve and refueling of the fuel tank until the fuel tankpressure falls below a threshold. In this way, safety during refuelingoperations may be enhanced.

If the vehicle is not running, then the controller may be configured toperform one or more leak detection routines for identifying the presenceof leaks in the fuel vapor recovery system. Specifically, leaks may beidentified by applying a vacuum and monitoring changes in fuel vaporrecovery system pressure (such as fuel tank pressure and canisterpressure). The vacuum applied for leak detection may be an engine-offnatural vacuum created due to a previous engine operation, or may beapplied by providing vacuum from the vacuum accumulator. In one example,where the leak is due to a degradation of a fuel vapor recovery systemvalve, such as the FTIV and/or the CPV, the controller may determinevalve degradation by comparing changes in the fuel tank pressure and/orthe canister pressure before and after the vacuum application.

To meet regulatory standards for fuel vapor recovery systems, the hybridvehicle may include one or more leak detection subroutines. In oneexample, during a first condition, wherein the hybrid vehicle has beenoperated in the engine-on mode for an extended duration the vehicletemperature may be high, generating a high pressure in the fuel tank,greater than a predetermine threshold, such as threshold₅ of FIG. 6,which is sufficient for leak detection. In the first condition, inanother example, the fuel tank pressure to be negative (a vacuum) asfuel stored in the fuel tank may have been consumed by the engine, suchthat the absolute value of the fuel tank pressure is greater than apredetermined threshold (such as threshold₅ of FIG. 6), and issufficient for leak detection.

If a high pressure or vacuum is present in the fuel tank (greater than athreshold), the fuel tank pressurization may be advantageously used totest for leaks in the system and identify degradation of the fuel vaporrecovery system components, such as the FTIV, the CPV, and/or the CVV,in a primary leak detection subroutine. For example, with the fuel tanksealed (by closing the FTIV and CPV) and pressurized, a rate of changeor pressure in the sealed fuel tank may be monitored. As such, in theabsence of leaks, the fuel tank pressure may be substantially constant,and may not fluctuate. Thus, in one example, the controller maydetermine degradation of one or more of the FTIV, the refueling valve,and/or the FTPT in a response to a rate of change of the fuel tank beinggreater than a threshold (such as threshold₆ of FIG. 6) due to one ormore leaks in the valves of the fuel tank or malfunction of the fueltank pressure sensor. If the pressure of the fuel tank did notsubstantially change, the FTIV may be commanded open such that air/fuelvapors are permitted to move through the vapor line, and the fuel tankpressure may be monitored again. As such, upon opening the FTIV, in theabsence of leaks, the fuel tank pressure may be expected to decreasesover time, for example decrease with a rate of change of fuel tankpressure greater than a threshold (such as threshold_(s) of FIG. 6), dueto the flow of vapors through the vapor line, If the rate of change ofthe fuel tank pressure is less than the threshold, the controller maydetermine that the FTIV is stuck in a closed position, and thus the FTIVis degraded.

As such, if the FTIV is functional, the canister pressure and the fueltank pressure can be expected to generally reach equilibrium. Forexample, the fuel tank pressure may gradually decrease towards thecanister pressure, while the canister pressure may gradually increasetowards the fuel tank pressure. Thus in another example, the controllermay determine degradation in one or more of the CPV, the CVV, and/or theCPT based on the rate of change of the canister pressure being greaterthan a threshold (threshold₁₀) after a predetermined duration of timehas elapsed. Upon indication of degradation of any of the abovementioned fuel vapor recovery system components, the controller may seta diagnostic code.

Optionally, in another example, the controller may generate the firstcondition, such that a vacuum or pressure sufficient for leak detectionis generated in the fuel tank. In one example, this may be accomplishedby allowing the engine to run after the vehicle has stopped to generatevacuum in the fuel tank through fuel consumption, or pressure byincreased vehicle temperature. In another example, the controller maydelay emission leak check for a predetermined duration and monitortemperature change during the duration of the delay, until temperaturechange is greater than a predetermined threshold (such as threshold₈ ofFIG. 7). The controller may then monitor fuel tank pressure and ifcorresponding change in pressure has not occurred with the change intemperature, degradation of one or more of the FTIV, the refuelingvalve, and/or the FTPT is determined by the controller. Each of theseexamples may allow for the primary leak detection subroutine to beimplemented by the controller, as described above.

In yet another example, during a second condition, wherein the hybridvehicle has been operated in the engine-off mode for an extendedduration, the vehicle temperature may be close to ambient temperatureand fuel consumption may be low. In this example, neither of a highpressure nor a vacuum are generated in the fuel tank and the fuel tankpressure may be less than a predetermine threshold (such as threshold₅of FIG. 6), and is insufficient for leak detection.

If a high pressure or vacuum is not present in the fuel tank (less thana threshold), an external vacuum source, such as a vacuum accumulator,may be advantageously used to test for leaks in the system and identifydegradation of the fuel vapor recovery system components, such as theFTIV, the CPV, and/or the CVV, in a secondary leak detection subroutine.The vacuum accumulator may obtain negative pressure/vacuum by one ormore methods. For example, the vacuum accumulator may be coupled to theengine intake manifold such that negative pressure is stored while thevehicle is operated in the engine-on mode. As such, the presence of avacuum may be dependent on engine-on operation time. Optionally, thecontroller may command the engine to run after the vehicle is shut offto increase engine-on time and increase the amount of vacuum stored inthe vacuum accumulator. In another example, vacuum accumulation may beindependent of engine-on time. As such, the vacuum accumulator may becoupled to a venturi located at a position on or within the vehicle thatreceives air flow, such as on the underside of the vehicle, or in theexhaust pathway of a brake booster pump. It may be appreciated that oneor more of the above methods may be used to accumulate vacuum for use inthe secondary leak detection subroutine.

As such, in the secondary leak detection subroutine, with the canistersealed (by closing the FTIV, CVV and CPV) and pressurized by applying avacuum from the vacuum accumulator via opening of the VAV, a rate ofchange or pressure in the sealed canister may be monitored. Thereby inthe absence of leaks, for example, the canister pressure may besubstantially constant, and may not fluctuate. Thus, in one example, thecontroller may determine degradation of one or more of the FTIV, theCVV, the CPV, and/or the CPT in a response to a rate of change of thefuel tank being greater than a threshold (such as threshold₁₀ of FIG. 8)due to one or more leaks in the valves of the canister or malfunction ofthe canister pressure sensor. If the pressure of the canister did notsubstantially change, the FTIV may be commanded open such that air/fuelvapors are permitted to move through the vapor line, and the canisterpressure may be monitored again. As such, upon opening the FTIV, in theabsence of leaks, the canister pressure may be expected to increase overtime, for example increase with a rate of change of canister pressuregreater than a threshold (such as threshold₁₀ of FIG. 8), due to theflow of vapors through the vapor line. If the rate of change of thecanister pressure is less than the threshold, the controller maydetermine that the FTIV is stuck in a closed position, and thus the FTIVis degraded.

As such, if the FTIV is functional, the canister pressure and the fueltank pressure can be expected to generally reach equilibrium. Forexample, the fuel tank pressure may gradually decrease towards thecanister pressure, while the canister pressure may gradually increasetowards the fuel tank pressure. Thus in another example, the controllermay determine degradation in one or more of the refueling vavle and/orthe FTPT based on the rate of change of the fuel tank pressure beinggreater than a threshold (threshold₆) after a predetermined duration oftime has elapsed. Upon indication of degradation of any of the abovementioned fuel vapor recovery system components, the controller may seta diagnostic code.

As discussed above, during leak detection, an order of detecting leaksin the components of the fuel vapor recovery system may be adjustedbased on the availability of sufficient pressure and/or vacuum in thefuel tank (such as, an engine-off natural vacuum) or an amount of vacuumthat may be supplied by the vacuum accumulator. Herein, two example leakdetection routines are depicted in FIGS. 6-8. A primary leak detectionroutine 600 may use pressure or vacuum from the fuel tank to detectleaks in a first order of detection including first determining thepresence of leaks in the fuel tank and then applying the pressure/vacuumfrom the fuel tank to the canister to determine the presence of leaks inthe canister. A secondary leak detection subroutine 800 may detect leaksin a second, alternate, order of detection including using vacuum froman external source (such as the accumulator) applied to the canister tofirst determine the presence of leaks in the canister and then applyingthe vacuum to the fuel tank to determine the presence of leaks in thefuel tank. Various sources and methods may be used to apply a vacuum orpressure to the canister and/or the fuel tank, as elaborated in FIG. 8.Maps of example pressure and temperature signals that may be received bythe controller during the leak detection routines of FIGS. 6-8 are shownin FIGS. 9-12.

Returning to FIG. 6, it shows a primary leak detection routine 600.Starting at 602, the controller may first estimate a fuel tank pressure(for example, based on a signal received from the FTPT) and determine ifthere is sufficient pressure or vacuum in the fuel tank to perform leakdetection. In one example, sufficient pressure or vacuum may bedetermined based on an absolute value of the fuel tank pressure beinggreater than a predetermined threshold (threshold₅). Herein, theabsolute fuel tank pressure may refer to an amount of positive pressurein the fuel tank, when the leak detection is performed by applyingpositive pressure, or may refer to an amount of vacuum in the fuel tank,when the leak detection is performed by applying a vacuum (that is,negative pressure).

Map 1000 in FIG. 10 depicts example ranges of acceptable absolute fueltank pressures and thresholds for leak detection based on whether theleak detection includes applying a positive pressure or a vacuum.Herein, threhold₅ extends equally in both directions of vacuum andpositive pressure application (as shown by dotted-lines) on each side ofthe x-axis, depicted as range 1010. In alternate embodiments, differentthresholds may be applied depending on whether a positive pressure or avacuum is applied during leak detection.

Each of the curves 1002, 1004, 1006, and 1008 represent example fueltank pressures. In the present embodiment, the absolute fuel tankpressure signal may be monitored and not a rate of change of fuel tankpressure. The controller may take detect the absolute pressure signal atvarious points in time, such as t₀, t₁, t₂, t₃, t₄, or t_(n). Based onthe absolute fuel tank pressure determined at a time when leak detectionis requested, the controller may determine whether to perform theprimary leak detection routine, including detecting leaks in the fueltank before detecting leaks in the canister, or whether to perform thesecondary leak detection routine, including detecting leaks in the fueltank after detecting leaks in the canister. In this example, a signaldetected at t_(n) is further described, wherein t_(n) is the time atwhich the controller receives an indication for leak detection may beenabled, such as shutting off of the vehicle and/or time elapsed sincelast leak detection event.

In one example, at 602, the absolute fuel tank pressure estimated att_(n) may be a positive pressure that is less than threshold₅ (as shownin curve 1004) or a vacuum that is greater than threshold₅ (as shown incurve 1006). In response to insufficient absolute pressure in the fueltank estimated at 602, the primary leak detection routine 600 may bedisabled by the controller at 603, and vacuum may be applied from one ormore alternative pressure and vacuum sources by enabling vacuumapplication routine 700 (shown in FIG. 7). If sufficient, vacuum isgenerated in the fuel tank in routine 700, 603 may loop back to thestart of the primary leak detection routine 600, starting at 602.Alternatively, at 605, a secondary leak detection routine with analternate order of leak detection (as elaborated in FIG. 8), may beenabled. In comparison, if the absolute fuel tank pressure estimated at602 is a positive pressure that is greater than threshold₅ (as shown incurve 1002) or a vacuum that is less than threshold₅ (as shown in curve1008), then in response to sufficient absolute pressure in the fueltank, the primary leak detection routine may continued.

Returning to FIG. 6, if sufficient pressure/vacuum is detected in thefuel tank, at 604, the fuel tank pressure may be monitored over time.That is, a change in fuel tank pressure over time (or a rate of changeof fuel tank pressure) may be monitored. At 606, it may be determinedwhether the change in fuel tank pressure over time is less than athreshold (threshold₆). As such, since the fuel tank remains sealedduring leak detection, a change in fuel tank pressure over time may beindicative of a leak at the fuel tank isolation valve (due to FTIVdegradation) and/or degradation of the FTPT. Thus, if the change in fueltank pressure over time is more than the threshold, at 608 FTIVdegradation may be determined and at 626, a diagnostic code may be set.If the change in fuel tank pressure over time is less than thethreshold, then at 610, the controller may determine that no leaks arepresent, and that the valves are not degraded.

Examples of changes in fuel tank pressure over time are shown in map 900of FIG. 9. Herein, the controller monitors changes in fuel tank pressure(by receiving signals from the FTPT) beginning at t₀ and continuing fora predetermined duration, herein to t_(n). Line 904 depicts a fuel tankpositive pressure that decreases over time and line 906 depicts a fueltank vacuum that increases over time. In this example, each of lines 904and 906 indicate the presence of leaks due to a change in fuel tankpressure over time that is greater than a threshold. In comparison, line902 shows a fuel tank positive pressure and line 908 shows a fuel tankvacuum that change over time at a rate lower than the threshold. Herein,each of lines 902 and 908 may indicate that there are no leaks in thesystem and that the valves of the fuel vapor recovery system are notdegraded.

Returning to FIG. 6, after it is determined that no leaks are present inthe fuel tank and the FTPT is operative, the controller may close theCVV and open the FTIV at 612, thereby sealing the canister from theatmosphere and applying the pressure or vacuum from the fuel tank to thecanister by allowing flow of air and fuel vapors through the vapor line.The CPV may be maintained in a closed position, as no purging operationsmay occur when the vehicle is off (see FIG. 3). At 614, a change inabsolute fuel tank pressure over time may again be monitored by thecontroller by receiving signals from the FTPT, and it may be determinedif the rate of change of absolute fuel tank pressure is greater than athreshold (threhsold₇). Herein, in the absence of leaks, after openingthe FTIV, the flow of fuel vapors from the fuel tank to the canister maybe expected to cause the fuel tank pressure to change. Thus, if thechange in fuel tank pressure over time is below the threshold, then at616, the controller may determine that a leak is present, and that theFTIV is degraded (e.g. is inoperative) and may set a diagnostic code at626. However, if the change in fuel tank pressure over time is greaterthan threshold, then at 618 the controller may determine that the FTIVis not degraded.

At 620, the controller may then monitor the canister pressure over timethrough signals from the CPT beginning at t_(o) and continuing for apredetermined duration (such as, to t_(n)), and a rate of canisterpressure change is determined at 622. For example, it may be determinedif the canister is able to hold pressure or vacuum over time after thefuel tank and the canister have equalized. At 628, the controller maydetermine that there is no leak in the canister based on a rate ofchange in canister pressure over time being less than a threshold(threshold₁₀). In one example, no leaks may be determined in the systemas the change in canister pressure is less than thershold₁₀, such assample pressures line 902 and line 908 of FIG. 9. In comparison, at 624,leaks may be determined in response to the change in canister pressureover time being greater than a threshold₁₀, such as sample pressurereadings line 904 and line 906 of FIG. 9. The controller may determinethe presence of a leak in the canister, degradation of a canister purgevalve, or CPT degradation, and set a diagnostic code at 626.

If at 602 the absolute value of fuel tank pressure is less thanthreshold₅, such as sample pressure readings line 1004 and line 1006 ofFIG. 10, then one or more alternate pressure/vacuum generation routinesmay be implemented by the controller, as now explained with reference toFIG. 7. One or more of the various vacuum generating strategiesdescribed herein may be either operated at different times, orconcurrently. In one example, when the first vacuum generating strategyis performed and a fuel tank temperature is measured, the second andthird strategies may be disabled. In another example, when engineoperation is continued in the second strategy, engine vacuum may bestored in the accumulator and applied for leak detection, as in thethird strategy. However, in alternate embodiments, only one of theengine vacuum (directly from the engine) or vacuum from the accumulatormay be enabled for leak detection. That is, when engine operation iscontinued in the second strategy, the vacuum accumulator may be closedand the third strategy may be disabled.

In a first strategy, at 704, leak detection may be delayed and a fueltank temperature, such as from a fuel tank temperature sensor, may berecorded at t₀. After a predetermined duration of time, t_(n), haselapsed, the fuel tank temperature may again be recorded and thecontroller may determine if the temperature has heated or cooledsufficiently to generate a pressure change in the fuel tank. This isrepresented in 710 as the absolute value of the change in temperaturebetween t₀ and t_(n) being greater than a threshold (threshold₈). In oneexample, threshold₈ may be related to threshold₅, such that thetemperature change corresponds to an amount of pressure/vacuum that issufficient for leak detection.

Example fuel tank temperature readings, as received from fuel tanktemperature sensor, are shown in map 1200 of FIG. 12. Herein line 1202demonstrates a change from a relatively higher temperature to arelatively cooler temperature, thereby decreasing a pressure in the fueltank; while line 1206 demonstrates a relatively cooler temperaturechanging to a relatively warmer temperature, thereby increasing apressure in the fuel tank. Each of lines 1202 and 1206 show atemperature change greater than the threshold, thereby indicating to thecontroller that a corresponding, sufficient amount of pressure change,has occurred. In comparison, line 1204, which is generally flat,represents a temperature change that is less than the threshold, therebyindicating that a sufficient pressure change has not occurred.

Returning to FIG. 7, if the change in temperature (and thus acorresponding change in pressure) at 710 is not greater than thethreshold, the routine may return to 704 and continue to delay the leak.However, if the temperature change is greater than the threshold, at 712(as in 602), the controller may then determine if the absolute value ofthe fuel tank pressure is greater than a threshold (threshold₅). In oneexample, at 716, when the absolute fuel tank pressure remains belowthreshold₅, in response to no pressure change in conjunction with atemperature change, the controller may determine that leaks are presentin the system. For example, it may be determined that leaks are presentin the FTIV, or CPV, or that the FTPT is degraded. Accordingly, at 718,a diagnostic code may be set. If the absolute pressure of the fuel tankis greater than threshold₅ at 712, then at 813, the primary leakdetection routine (FIG. 6) may be resumed.

In a second vacuum generating strategy, beginning at 724, the controllermay close the CVV and maintain the closed position of the CPV and FTIV,such that the canister side of the circuit is sealed. Vacuum from avacuum accumulator is then applied to the canister by opening the VAV at726. The vacuum accumulator may acquire vacuum from one or more of theengine intake, an ambient air stream, or the brake booster exhaustpathway. At 728, the controller may determine if the canister pressureis less than a threshold, threhsold₉, by receiving a signal from theCPT. In one example at 729, wherein the canister pressure is less thanthreshold₉, a secondary leak detection routine (FIG. 8) may be enabled.If the canister pressure is greater than a threshold₉ upon applicationof a vacuum, at 730, the controller may determine that one or more ofthe canister valves, or FTIV, or CPT are degraded.

Example changes in canister pressure, as received from the CPT, areshown in map 1100 of FIG. 11. Herein, the dotted-line representsthreshold₉. In the present embodiment, the canister pressure is detectedat various points in time, such as t₀, t₁, t₂, t₃, t₄, or t_(n). Forthis example, a signal detected at t_(n) is further described, whereint_(n) is the time at which other signals are received by the controllerindicating that leak detection may be enabled, such as time elapsedsince opening of the VAV.

At t_(n), example CPT reading shown in line 1102 may be a positivepressure that is greater than threshold₉ and example CPT reading shownin line 1104 may be a vacuum that is greater than threshold₉. If at thetime that a vacuum is applied on the canister, the canister pressure isgreater than the threshold, as shown in line 1102 and line 1104, thesecondary leak detection routine 800 (FIG. 8) may be disabled by thecontroller and a diagnostic code may be set to report degradation of oneor more the canister valves and/or the CPT. In comparison, if at t_(n),the canister pressure shows that a canister vacuum is less thanthreshold₉, as shown in line 1106, the secondary leak detection routine800 (FIG. 8) may be enabled by the controller.

Returning to FIG. 7, in a third vacuum generating strategy, beginning at720, the engine may be run for a duration (such as a short duration)after the vehicle is shut off. The duration of the continued engineoperation may correspond to a length of time required to generatesufficient pressure/vacuum, for example, a duration required to bringthe absolute pressure in the fuel tank above a threshold (such asthreshold₅). If the engine is run after the vehicle is shut off andabsolute fuel tank pressure is less than threshold₅ (at 712), then at716, the controller may determine that a leak is present in the fueltank (e.g., due to FTIV degradation) and may set a diagnostic code at718. If the absolute value of fuel tank pressure is greater thanthreshold₅ at 712, the controller may initiate primary leak detectionroutine 600.

Optionally, alternative to generating a vacuum in the fuel tank, thecontinued engine operation at 720 may be used to store vacuum in avacuum accumulator, as in 722. In this case, the vacuum accumulator maybe coupled to the engine intake and vacuum may be applied to thecanister by opening of the VAV, as in 726. The routine may then returnto the second vacuum generating strategy (as previously elaborated at728-730). If sufficient vacuum is present in the canister (that is,canister pressure is less than threshold₉), then at 729, the secondaryleak detection routine 800 may be implemented by the controller, asshown in FIG. 8.

Now turning to FIG. 8, a secondary leak detection routine is depictedthat may be enabled in response to insufficient fuel tank pressure orvacuum for performing the primary leak detection routine. In thesecondary routine, the canister may be checked for leaks beforeconfirming operation of the FTIV, and detecting leaks in the fuel tank.Specifically, a vacuum may be applied from a source other thanengine-off natural vacuum, such as the vacuum generated in FIG. 7, andleak detection may be enabled in the canister before detecting leaks inthe fuel tank.

At 802, a vacuum is applied to the canister from a vacuum accumulatorsuch that the canister pressure is less than threshold₉ (as previouslyshown at 726 and 728 of FIG. 7). Once sufficient vacuum has beendetected in the canister, at 804, canister pressure is monitored overtime. At 806, it may be confirmed whether the change in canisterpressure over time is less than a threshold (threshold₁₀). As thecanister may remain sealed during leak detection, a change in canisterpressure over time being greater than a threshold at 806 may beindicative of a leak, for example, at one more of the canister valvesand/or degradation of the CPT (at 808), and a diagnostic code may be setby the controller at 826. A sample pressure reading indicating a leakmay be represented by line 906 of FIG. 9. If the change in canisterpressure over time is less than the threshold at 806, then at 810, thecontroller may determine that the valves of the canister have no leaksand the CPT is operative. A sample pressure reading indicating that noleak is present may be represented by line 908 of FIG. 9.

After it is determined that no leaks are present in the canister and theCPT is operative, the controller may open the FTIV at 812, therebyapplying the vacuum from the canister to the fuel tank by allowing flowof air and fuel vapors through the vapor line. The CPV may be maintainedin a closed position, as no purging operations may occur when thevehicle is off (see FIG. 3). At 814, a change in canister pressure overtime may again be monitored by the controller. If the change in canisterpressure over time is less than a threshold, the controller maydetermine that the FTIV is inoperative (e.g., is stuck closed) at 816,and may set a diagnostic code at 826. However, if a change in canisterpressure over time is greater than the threshold₁₀, then at 818, thecontroller may determine that the FTIV is operative (e.g., is not stuckopen), as in 818. In this case, line 908 of FIG. 9 may show no changeover time and may indicate malfunction of the FTIV, while line 906 mayshow change in pressure over time and may indicate that the FTIV isoperative.

At 820, the controller may monitor the fuel tank pressure over time, forexample, through signals from the FTPT, beginning at t₀ and continuingfor a predetermined duration to t_(n). The change in fuel tank pressureover time may be determined to be greater or less than a threshold(threshold₆) at 822. At 828, it may be determined by the controller thatthere is no leak if the change in fuel tank pressure over time is lessthan threshold₆. Specifically, a fuel tank pressure reading showinglittle or no change over time indicates that there are no leaks presentin the fuel tank, such as line 908 of FIG. 9. In comparison, a fuel tankpressure reading showing change over time indicates that there may be aleak present in the fuel tank, such as line 906 of FIG. 9. Accordingly,the controller may determine the presence of leaks at 824 and set adiagnostic code at 826, respectively. After diagnostic codes indicatingleaks are set by the controller, secondary leak detection subroutine 800may be ended.

In this way, leak detection routines may be adjusted based on theavailability of sufficient amount of pressure or vacuum for the leakdetection. Further, purging operations may be coordinated with refuelingoperations and leak detection operations, thereby improving fuel vapormanagement, particularly in hybrid vehicles.

It will further be appreciated that the configurations and routinesdisclosed herein are exemplary in nature, and that these specificembodiments are not to be considered in a limiting sense, becausenumerous variations are possible. For example, the above diagnosticroutines may be decoupled such that leak detection of the fuel tank andthe canister are performed as distinct operations. The subject matter ofthe present disclosure includes all novel and non-obvious combinationsand sub-combinations of the various systems and configurations, andother features, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations andsub-combinations regarded as novel and non-obvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereof.Such claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements. Other combinations and sub-combinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether broader, narrower,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

1. A method of operating a fuel vapor recovery system including a fueltank and a canister coupled to an engine intake, comprising, during apurging condition, purging a first amount of fuel vapors from thecanister to the engine intake; and after purging the first amount,purging a second amount of fuel vapors from the fuel tank to thecanister, the second amount adjusted based on the first amount.
 2. Themethod of claim 1, wherein the purging condition includes a canisterpressure being greater than a first threshold.
 3. The method of claim 2,wherein the fuel tank is coupled to the canister through a first valve,and the canister is coupled to the engine intake through a second valve,and wherein purging the first amount includes maintaining the firstvalve closed to isolate the fuel tank from the canister while openingthe second valve to couple the canister to the engine intake.
 4. Themethod of claim 3, wherein purging the second amount includes openingthe first valve to couple the fuel tank to the canister.
 5. The methodof claim 4, wherein during purging of the second amount, opening of thefirst valve is adjusted based on at least one of a canister pressure anda fuel tank pressure.
 6. The method of claim 5, wherein the adjustmentof the first valve includes opening the first valve when at least one ofthe canister pressure is lower than the first threshold and the fueltank pressure is greater than a second threshold.
 7. The method of claim6, wherein the fuel tank pressure is estimated by a first pressuresensor coupled to the fuel tank, and wherein the canister pressure isestimated by a second pressure sensor coupled to the canister.
 8. Themethod of claim 7, further comprising, after purging the second amount,closing the first valve.
 9. The method of claim 1, further comprising,in response to a request for refueling, delaying purging of the firstamount and the second amount at least until refueling is completed. 10.The method of claim 8, wherein completion of refueling is indicated byat least one of a fuel tank pressure exceeding a threshold, a refuelingdoor sensor indicating a refueling door being closed, and a fuel levelsensor exceeding a threshold, and wherein purging of the first or secondamount is initiated in response to the completion of refueling.
 11. Avehicle system, comprising, a battery; an engine including an engineintake, the engine selectively started and stopped responsive to abattery state of charge; a fuel system comprising, a fuel tank with afirst opening for receiving fuel and a second opening for deliveringfuel vapors along a first conduit; a canister with a first opening forreceiving air from an atmosphere, a second opening for receiving fuelvapors from the fuel tank along the first conduit, and a third openingfor relaying stored fuel vapors to an engine intake along a secondconduit; a vacuum accumulator including a venturi, the vacuumaccumulator coupled to the canister along the second conduit through avacuum accumulator valve; a fuel tank isolation valve, positioned in thefirst conduit, coupling the fuel tank to the canister; a canister purgevalve, positioned in the second conduit, coupling the canister to theengine intake; a canister vent valve coupled to the first opening of thecanister, a first pressure sensor in the first conduit for estimating afuel tank pressure; a second pressure sensor in the second conduit forestimating a canister pressure; and a control system with computerreadable instructions for, during a purging condition, when the canisterpressure is greater than a threshold, isolating the fuel tank whilepurging a first amount of fuel vapors from the canister to the engineintake; after purging the first amount of fuel vapors, coupling the fueltank and purging a second amount of fuel vapors from the fuel tank, thesecond amount adjusted based on the first amount; and after purging thesecond amount, isolating the fuel tank.
 12. The system of claim 11,wherein isolating the fuel tank includes closing the fuel tank isolationvalve and coupling the fuel tank includes opening the fuel tankisolation valve.
 13. The system of claim 12, wherein purging the firstamount includes opening the canister purging valve and the canister ventvalve.
 14. The system of claim 13, wherein purging the second amountincludes closing the canister purge valve and the canister vent valve topurge fuel vapors to the canister when the fuel tank pressure is below athreshold, and opening the canister purging valve and the canister ventvalve to purge fuel vapors to the engine intake when the fuel tankpressure is above a threshold.
 15. The system of claim 11, wherein thecontrol system further includes instructions for, in response to arequest for refueling, delaying purging until refueling is completed.16. The system of claim 15, wherein refueling includes, opening a fueltank door and receiving fuel in the fuel tank after the fuel tankpressure has dropped below a threshold.
 17. The system of claim 16,wherein a completion of refueling is indicated by at least one of thefuel tank pressure exceeding the threshold, a fuel door sensorindicating a refueling door is closed, and a fuel level sensor exceedinga threshold.
 18. The system of claim 11, wherein the purging conditionincludes the engine being in an engine-on mode of operation, and acanister pressure being greater than a threshold.
 19. A vehicle fuelvapor recovery system, comprising, a fuel tank coupled to a canisterthrough a fuel tank isolation valve, the fuel tank configured to receivefuel through a refueling door; a canister, configured to store fuelvapors, coupled to an engine intake through a canister purge valve, thecanister further coupled to a vacuum accumulator; a first pressuresensor coupled to the fuel tank to estimate a fuel tank pressure; asecond pressure sensor coupled to the canister to estimate a canisterpressure; and a control system with computer readable instructions for,during an engine-on mode of operation, opening the canister purge valvewhile closing the fuel tank isolation valve to purge a first amount ofstored fuel vapors to the engine intake when the canister pressure isgreater than a threshold; after purging the first amount of stored fuelvapors, opening the fuel tank isolation valve while closing the canisterpurge valve to purge a second amount of fuel vapors to the canister whenthe fuel tank pressure is greater than a first threshold; and afterpurging the first amount of stored fuel vapors, opening the fuel tankisolation valve while maintaining the canister purge valve open to purgethe second amount of fuel vapors to the engine intake when the fuel tankpressure is greater than a second threshold higher than the firstthreshold.
 20. The system of claim 19, wherein the control systemfurther includes instructions for, in response to a request forrefueling, delaying purging until refueling is completed, a completionof refueling indicated by a closing of the refueling door.
 21. Thesystem of claim 20, wherein a duration of delaying is adjusted based ona fuel level in the fuel tank and/or a fuel tank pressure afterrefueling, including delaying purging for a longer duration as the fuellevel and/or the fuel tank pressure increase during refueling.